Finger on the Weather

Storm talk: What is a ‘cap’ in the atmosphere, anyway?

Over the years, weather watchers have heard the term “cap” often when listening to meteorologists or storm chasers discuss a storm’s potential.

Usually, it’s within the context of a strong cap preventing the initiation of severe storms — or a cap eroding and thus allowing powerful storms to erupt. This graphic created by the Kansas City branch of the National Weather Service does a nice job of explaining how a cap develops.

In short, supercell thunderstorms won’t develop if air in the upper atmosphere is warmer than the air beneath it. The cap “erodes” when the temperatures close to the surface warm up enough to match the upper layer of warm air.

As the weather service said in explaining this graphic, even one degree can be the difference between a significant outbreak of severe weather and almost no storms at all.

Keep this graphic in mind as the spring storm season unfolds.

Reach Stan Finger at 316-268-6437 or Follow him on Twitter: @StanFinger.